THE PROPELLER REGIME OF DISK ACCRETION TO A RAPIDLY ROTATING MAGNETIZED STAR

Authors: M.M. Romanova, G.V. Ustyugova, A.V. Koldoba,  R.V.E. Lovelace. 

The propeller regime of disk accretion to a rapidly rotating magnetized star is investigated here for the first time by axisymmetric 2.5D magnetohydrodynamic simulations. An expanded, closed magnetosphere forms in which the magnetic field is predominantly toroidal. A smaller fraction of the star's poloidal magnetic flux inflates vertically, forming a magnetically dominated tower. Matter accumulates in the equatorial region outside magnetosphere and accretes to the star quasi-periodically through elongated funnel streams which cause the magnetic field to reconnect. The star spins-down owing to the interaction of the closed magnetosphere with the disk. For the considered conditions, the spin-down torque varies with the angular velocity of the star W* as ~w*1.3 for fixed mass accretion rate. The propeller stage may be important in the evolution of X-ray pulsars, cataclysmic variables and young stars. In particular, it may explain the present slow rotation of the classical T Tauri stars.

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Last updated on 29.01.07